1. Field of the Invention
The invention relates to technology of an injection molding apparatus that, after closing a mold, injecting molten resin material or the like into the mold, setting the resin material or the like, and opening the mold, extrudes the molded resin using an ejector pin, and relates to technology of an injection molding method that, after closing a mold, injecting molten resin material or the like into the mold, setting the resin material or the like, and opening the mold, extrudes the molded resin using an ejector pin.
2. Description of the Related Art
Injection molding using an injection molding apparatus is performed when molding a work with resin. This kind of injection molding is used, for example, when molding an insert coil with thermosetting resin in order to improve radiation performance of the insert coil that serves as a work 170, as shown in FIG. 11 (see reference character 170 in FIG. 11).
An injection molding apparatus 110 that performs this kind of injection molding includes a fixed die 120, a movable die 130, an ejector plate 135, and ejector pins 140 and the like, as shown in FIG. 12A. The movable die 130 is able to move closer to and farther away from the fixed die 120. The ejector plate 135 is arranged inside the movable die 130, and is able to move toward the fixed die 120 by being driven by an ejector rod 136. The ejector plate 135 is urged away from the fixed die 120 by a spring 144 provided on one of the ejector pins 140. As shown in FIG. 12B, one end portion of each of the ejector pins 140 is inserted through a corresponding pin hole 132 formed in the movable die 130, and the other end portion of each of the ejector pins 140 is supported by the ejector plate 135. The one end surface of each of the ejector pins 140 is arranged in line with an end surface of the movable die 130 (i.e., flush with the end surface of the movable die 130).
With the injection molding apparatus 110 structured in this way, the mold is closed by bringing the movable die 130 that supports the work 170 toward the fixed die 120. Then molten resin 160 is injected from the fixed die 120 and set. Also, the mold is opened by moving the movable die 130 away from the fixed die 120, as shown in FIG. 13A. After opening the mold, portions corresponding to a gate portion and a runner portion and the like of the resin 160 are extruded by driving the ejector rod 136 to make the ejector pins 140 protrude out of the pin holes 132, as shown in FIG. 13B. Then, a portion corresponding to a cavity portion of the resin 160 is extruded, as shown in FIG. 14A. Next, the ejector rod 136 stops being driven, such that the ejector pins 140 are returned by the spring 144 to the positions they were in before extruding the resin 160. It is in this way that the injection molding apparatus 110 performs injection molding.
With this kind of injection molding apparatus 110, when injecting the resin 160, there is a possibility that the ejector pins 140 may not return all the way to the positions they were in before extruding the resin 160 due to the resin 160 getting into a clearance 145 (see FIG. 12B) formed between the ejector pins 140 and the pin holes 132. That is, there is a possibility that the ejector pins 140 may remain protruding out from the pin holes 132, as shown in FIG. 14B. Also, greater force is needed to make the ejector pins 140 protrude out from the pin holes 132, so there is chance that a molded article 171 may not be able to be extruded. With such an injection molding apparatus 110, an operational problem results from the resin 160 getting into the clearance 145. In this case, the injection molding apparatus 110 requires maintenance to remove the resin 160 that has gotten into the clearance 145.
Japanese Patent Application Publication No. 7-266367 (JP-A-7-266367) describes an injection molding apparatus that solves this problem.
The injection molding apparatus described in JP-A-7-266367 performs maintenance molding by performing injection molding with the ejector pins arranged in positions that are retracted farther than the positions where normal injection molding has been performed (i.e., in positions away from the molded article), after injection molding such as that described above has been performed a predetermined number of times. As a result, resin that gets into the clearance is removed.
However, with the injection molding apparatus described in JP-A-7-266367, the amount of resin used increases by the amount used for the maintenance molding, so the injection molding manufacturing cost ends up increasing. From the viewpoint of manufacturing cost, it is conceivable to reduce the frequency with which the maintenance molding is performed, that is, perform maintenance molding after normal injection molding has been performed a greater number of times, but this may result in resin getting into the clearance. That is, the likelihood that there will be an operational problem with the injection molding apparatus, such as that described above, would increase.